Method of preparing a foamed molded article and blow-filling gun apparatus for use therein

Abstract

A method of molding pre-foamed synthetic resin particles is described, which comprises increasing the pressure in a mold cavity with a pressurized gas, charging the mold cavity with pre-foamed synthetic resin particles as they are compressed with a gas pressurized to a pressure higher than the pressure in the mold cavity and heating the charged pre-foamed synthetic resin particles with steam so that they are fused together or expanded and fused together to form a foamed molded article, wherein a pressure detector is provided in a conduit for conveying the pre-foamed synthetic resin particles into the mold cavity as they are carried by the pressurized gas or at an inlet portion of a charging port leading to the mold cavity, and the supply of pre-foamed synthetic resin particles into the mold cavity is stopped when the pressure detected by the detector exceeds the pressure in the mold cavity by a predetermined amount. A blow-filing gun apparatus suitable for use in the practice of the molding method is also described.

What is claimed is: 
     
       1. A method of molding pre-foamed synthetic resin particles into a foamed molded article, which comprises the steps of: increasing the pressure in a mold cavity having a charging port with a pressurized gas;   charging said mold cavity with pre-foamed synthetic resin particles as they are compressed with a gas pressurized to a pressure higher than the pressure in the mold cavity through a conduit into the mold cavity;   controlling said charging such that the supply of pre-foamed resin particles is stopped when the pressure within said conduit or said charging port, as detected by a pressure sensitive switch, exceeds the pressure in the mold cavity by a predetermined amount; and   heating the charged pre-foamed synthetic resin particles with steam so that they are fused together or expanded and fused together to form a foamed molded article.   
     
     
       2. The method according to claim 1, wherein said pressure sensitive switch is provided in the conduit which conveys the pre-foamed synthetic resin particles into the mold cavity as the particles are carried by said pressurized gas. 
     
     
       3. The method according to claim 2, wherein the supply of pre-foamed synthetic resin particles into the mold cavity is stopped when the pressure detected by said detector exceeds the pressure in the mold cavity by 0.2 to 1 kg/cm 2 . 
     
     
       4. The method according to claim 2 or 3, wherein the pre-foamed synthetic resin particles are supplied into the mold cavity at intervals in successive portions. 
     
     
       5. The method according to claim 1, wherein said pressure detector is provided at the inlet portion of a charging port leading to the mold cavity. 
     
     
       6. The method according to claim 5, wherein the supply of pre-foamed synthetic resin particles into the mold cavity is stopped when the pressure detected by said detector exceeds the pressure in the mold cavity by 0.2 to 1 kg/cm 2 . 
     
     
       7. The method according to claim 5 or 6, wherein the pre-foamed synthetic resin particles are supplied into the mold cavity at intervals in successive portions. 
     
     
       8. The method according to claim 1, wherein said pressure in the mold cavity is at least 0.1 to 6.0 kg/cm 2  G. 
     
     
       9. The method according to claim 1, wherein said pre-foamed synthetic resin particles are selected from the group consisting of pre-foam polypropylene particles and pre-foamed crosslinked polyethylene particles, which maintain atmospheric pressure (0 kg/cm 2  G) in the interior of the cells. 
     
     
       10. The method according to claim 1, wherein said pre-foamed synthetic resin particles are selected from the group consisting of pre-foamed polypropylene particles and pre-foamed crosslinked polyethylene particles which have been pressurized with a pressurized gas and aged to increase the pressure in the cells to at least 0.5 kg/cm 2  G. 
     
     
       11. The method according to claim 9, wherein said pre-foamed synthetic resin particles have a compression ratio of from 40 to 65%. 
     
     
       12. the method according to claim 10, wherein said pre-foamed synthetic resin particles have a compression ratio ranging from 10 to 20%. 
     
     
       13. A blow-filling gun apparatus for charging pre-foamed synthetic resin particles into a mold cavity, which comprises: a main opening that communicates with a charging port leading to said mold cavity;   a branched opening that communicates with a conduit for conveying said pre-foamed synthetic resin particles to said mold cavity;   a sheathed blow-filling gun cylinder comprised of an inner pipe concentrically disposed within an outer pipe and spaced apart from said outer pipe, said cylinder connecting said charging port leading to the mold cavity to said main opening; and   a plunger that is capable of closing and charging port leading to the mold cavity, said space between said inner and outer pipes of said sheathed blow-filling gun cylinder communicating with the inlet portion of said charging port leading to the mold cavity, and a pressure sensitive switch being mounted in the space between the inner and outer pipes of said sheathed blow-filling filling gun cylinder.